Bag-in-containers, also referred to as bag-in-bottles or bag-in-boxes depending on the geometry of the outer vessel, all terms considered herein as being comprised within the meaning of the term bag-in-container, are a family of liquid dispensing packaging consisting of an outer container comprising an opening to the atmosphere—the mouth—and which contains a collapsible inner bag joined to said container and opening to the atmosphere at the region of said mouth. The system must comprise at least one vent fluidly connecting the atmosphere to the region between the inner bag and the outer container in order to control the pressure in said region to squeeze the inner bag and thus dispense the liquid contained therein.
Traditionally, bag-in-containers were—and still are—produced by independently producing an inner bag provided with a specific neck closure assembly and a structural container (usually in the form of a bottle). The bag is inserted into the fully formed bottle opening and fixed thereto by means of the neck closure assembly, which comprises one opening to the interior of the bag and vents fluidly connecting the space between bag and bottle to the atmosphere; examples of such constructions can be found infer alia in U.S. Pat. Nos. 3,484,011, 3,450,254, 4,330,066, and 4,892,230. These types of bag-in-containers have the advantage of being reusable, but they are very expensive and labour-intensive to produce.
More recent developments focused on the production of “integrally blow-moulded bag-in-containers” thus avoiding the labour-intensive step of assembling the bag into the container, by blow-moulding a polymeric multilayer preform into a container comprising an inner layer and an outer layer, such that the adhesion between the inner and the outer layers of the thus produced container is sufficiently weak to readily delaminate upon introduction of a gas at the interface. The “inner layer” and “outer layer” may each consist of a single layer or a plurality of layers, but can in any case readily be identified, at least upon determination. Said technology involves many challenges and many alternative solutions were proposed.
The multilayer preform may be extruded or injection moulded (cf. U.S. Pat. No. 6,238,201, JPA10128833, JPA11010719, JPA9208688, U.S. Pat. No. 6,649,121. When the former method is advantageous in terms of productivity, the latter is preferable when wall thickness accuracy is required, typically in containers for dispensing beverage.
Preforms for the production of integrally blow-moulded bag-in-containers clearly differ from preforms for the production of blow-moulded co-layered containers, wherein the various layers of the container are not meant to delaminate, in the thickness of the layers. A bag-in-container is comprised of an outer structural envelope containing a flexible, collapsible bag. It follows that the outer layer of the container is substantially thicker than the inner bag. This same relationship can of course be found in the preform as well, which are characterized by an inner layer being substantially thinner than the outer layer. Moreover, in some cases, the preform already comprised vents which are never present in preforms for the production of co-layered containers (cf. EPA1356915).
The formation of the vents fluidly connecting the space or interface between bag and bottle to the atmosphere remains a critical step in integrally blow-moulded bag-in-containers and several solutions were proposed in e.g., U.S. Pat. Nos. 5,301,838, and, 5,407,629, JPA5213373, JPA8001761, EPA1356915, U.S. Pat. No. 6,649,121, JPA10180853. One redundant problem with integrally blow-moulded bag-in-containers is the choice of materials for the inner and outer layers which must be selected according to strict criteria of compatibility in terms of processing on the one hand and, on the other hand, of incompatibility in terms of adhesion. These criteria are sometimes difficult to fulfil in combination as illustrated below. The thermal properties of the materials of the inner and outer layers should be as close as possible for the blow-moulding step, but should differ sufficiently for the injection moulding production of an integral multilayer preform.
Beside the thermal properties, it should be ensured that the inner and outer layers form a weak interface to ensure proper delamination of the inner layer from the outer layer upon use; JP2005047172 states that the inner and outer layers should be made of “mutually non-adhesive synthetic resins.”
As an interface between inner and outer layer is inevitably formed upon blow-moulding, which strength may not always be as uniform as one could desire, due to various phenomena during the blow-moulding stage, such as local heat gradients, differential resin stretch and flow rates at different points of the vessel, etc., the delamination of the inner bag from the outer layer is not always perfectly controllable. It has been observed that the two layers may delaminate preferentially on one side of the bag-in-container due to a local weakness of the interface and, as the bag starts shrinking asymmetrically bending and folding with the risk of forming pockets full of liquid separated from the container's mouth. If this happens, the bag-in-container cannot be used anymore although it can still contain a considerable amount of liquid.
JP4267727 suggests to fix the inner and outer layers at their bottoms without disclosing how to achieve this. In Japanese Utility Model JP048519, one end of a co-extruded multilayer parison is pinched off such that mutually engaging corrugations are formed, and fixing the structure through an additional device prior to blow-moulding. U.S. Pat. No. 6,649,121 proposes to fix the inner bag to the outer layer by forming at the bottom of the inner layer of the preform to be blow-moulded into the bag-in-container, a protrusion which fits a through hole formed at the bottom of the outer layer and engages mechanically on the outer surface of the outer layer. This geometry appears to be maintained through the blow-moulding process by limiting the axial stretch of the bottom area of the container through the driving downwards of a stretching rod.
Co-extruded parisons as described is the foregoing Japanese Utility Model do not allow the same wall thickness control as when injection moulded preforms are used, which is required is applications in the field of pressurized beverage dispense bag-in-containers. The solution proposed in U.S. Pat. No. 6,649,121 applies to bag-in-containers wherein the liquid contained in the bag is dispensed by decreasing the pressure in the bag and does not allow to dispense liquid by injection of a pressurized gas at a point of the interface between the inner and outer layers because the inner layer's protrusion is not meant to engage hermetically on the outer surface of the outer layer. Indeed, the solution proposed in U.S. Pat. No. 6,649,121 includes that air must penetrate through the interstice between the protrusion and the through hole wall to compensate for the growing pressure drop as a gap is formed between the inner and outer layers upon extracting the liquid by vacuum and the resuming shrinking of the bag.
It follows from the foregoing that there remains a need in the art for an integrally blow-moulded bag-in-container that allows controlled delamination of the inner bag from the outer container upon injection of a pressurized gas at the interface thereof.